[英]Select parts of one table and count rows of another
我有2個MySQL表:人和連接
我想從人員中選擇所有列,並計算他們在連接表中有多少連接。
-------------------- ----------------------
| People | | Connections |
-------------------- ----------------------
| person_id | name | | cnt_id | person_id |
-------------------- ----------------------
我想從人員中選擇所有人,並選擇該人的person_id在第二個表中出現的次數。
我一直想弄明白,但不能。 希望你們都能提供幫助。
謝謝!
如果有人沒有連接,這將給出一個零計數的行:
SELECT
People.person_id,
People.name,
COUNT(Connections.person_id) AS number_of_connections
FROM People
LEFT JOIN Connections
ON People.person_id = Connections.person_id
GROUP BY People.person_id
嘗試這個
SELECT name,count(Connection.person_id) as cnt FROM
People LEFT JOIN Connection ON People.person_id = Connection.person_id
GROUP BY Connection.person_id
聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.